The Apostle of Allah ﷺ saw sputum sticking to the Qibla of the mosque. He scratched it off with a pebble and then forbade spitting on the right side or in front, but (it is permissible) to spit on the left side or under the left foot.
أَنَّ النَّبِيَّ ﷺ رَأَى نُخَامَةً فِي قِبْلَةِ الْمَسْجِدِ فَحَكَّهَا بِحَصَاةٍ ثُمَّ نَهَى أَنْ يَبْزُقَ الرَّجُلُ عَنْ يَمِينِهِ أَوْ أَمَامَهُ وَلَكِنْ يَبْزُقُ عَنْ يَسَارِهِ أَوْ تَحْتَ قَدَمِهِ الْيُسْرَى